Smart Tetraphenylethene‐Based Luminescent Metal–Organic Frameworks with Amide‐Assisted Thermofluorochromics and Piezofluorochromics

Abstract Luminescent metal–organic frameworks (MOFs) are appealing for the design of smart responsive materials, whereas aggregation‐induced emission (AIE) fluorophores with twisted molecular rotor structure provide exciting opportunities to construct MOFs with new topology and responsiveness. Herein, it is reported that elongating AIE rotor ligands can render the newly formed AIE MOF (ZnETTB) (ETTB = 4',4''',4''''',4'''''''‐(ethene‐1,1,2,2‐tetrayl)tetrakis(([1,1'‐biphenyl]‐3,5‐dicarboxylic acid))) with more elasticity, more control for intramolecular motion, and specific amide‐sensing capability. ZnETTB shows specific host–guest interaction with amide, where N,N‐diethylformamide (DEF), as an example, is anchored through C—H···O and C—H···π bonds with Zn cluster and ETTB8− ligand, respectively. DEF anchoring reduces both the distortion level and the intramolecular motions of ETTB8− ligand to lead a blueshifted and intensified emission for DEF ∈ ZnETTB. Moreover, amide anchoring also affords the DEF ∈ ZnETTB with the excellent thermofluorochromic behavior, and further increases the piezofluorochromic sensitivity at low‐pressure ranges on the basis of its elastic framework. This work is one of the rare examples of amide‐responsive smart materials, which shall shed new lights on design of smart MOFs with twisted AIE rotors for further sensing and detection applications.


Table of Contents: Experimental Section
Supporting Tables  Table S1 Crystallographic data of the ZnTCPE. Table S2 Selected bond lengths (Å) and angles (°) of ZnTCPE.

Figure S4
The simulated and experimental PXRD spectra of Solv.∈ZnETTB.

Figure S8
(a) N 2 adsorption isotherm of ZnETTB at 77 K. (b) Pore size distribution of ZnETTB obtained under N 2 adsorption conditions.

Figure S15
Cyclic switching of the solid-state fluorescence emission wavlength and intensity of Solv.∈ZnETTB and ZnETTB. Figure S16 PXRD of ZnETTB crystals after soaking in different organic solvents. Figure S17 Fluorescence lifetime of DEF∈ZnETTB and ZnETTB.

Figure S18
(a) Solid-state fluorescence spectra of crystal DEF∈ZnETTB upon increasing hydrostatic pressure from 1 atm (101 kPa) to 10.63 GPa. (b) Solid-state fluorescence spectra of DEF∈ZnETTB upon reducing hydrostatic pressure.

Figure S20
(a) Photographs of DEF∈ZnTCPE crystals under UV irradiation upon increasing or reducing hydrostatic pressure. (b) Solid-state fluorescence spectra of crystal DEF∈ZnTCPE upon increasing hydrostatic pressure from 1 atm (101 kPa) to 10.74 GPa. (c) Fluorescence spectra of DEF∈ZnTCPE upon reducing hydrostatic pressure.

Figure S22
Photographs of the ZnETTB crystals under UV irradiation upon (a) increasing or (b) reducing hydrostatic pressure. Figure S23 Solid-state fluorescence spectra of ZnETTB upon reducing hydrostatic pressure.

Single-crystal X-ray crystallography.
Diffraction data for the complex were collected on a Bruker SMART CCD diffractometer (Cu-Kα radiation and λ = 1.54184 Å) in Φ and ω scan modes. The structures were solved by direct methods, followed by difference Fourier syntheses, and then refined by full-matrix least-squares techniques on F 2 using SHELXL and Olex2. 1 All other non-hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms were placed at calculated positions and isotropically refined using a riding model. Tables S1 ~ S6 summarizes X-ray crystallographic data and refinement details for the   O004-Zn01-O00C iii 75.0(2) O003 iv -Zn02-O008 108.5(2) O006 ii -Zn02-O008 99.9(3)  Figure S1. The simulated and experimental powder X-ray diffraction (PXRD) spectra of Solv.∈ ZnTCPE.                 Figure S17. Fluorescence lifetime of DEF∈ZnETTB and ZnETTB.